Golf club heads come in many different forms and makes, such as wood- or metal-type, iron-type (including wedge-type club heads), utility- or specialty-type, and putter-type. Each of these styles has a prescribed function and make-up.
Iron-type golf clubs generally include a front or striking face, a top line, and a sole. The front face interfaces with and strikes the golf ball. A plurality of score lines or grooves is provided on the face to assist in imparting spin to the ball. The top line is generally configured to have a particular look to the golfer and to provide weight. The sole of the golf club is particularly important to the golf shot because it contacts and interacts with the ground during the swing.
In conventional sets of iron-type golf clubs, each club includes a shaft with a club head attached to one end and a grip attached to the other end. The club head includes a face for striking a golf ball. The angle between the face and a vertical plane is called the loft angle.
The set generally includes irons that are designated number 3 through number 9, and a pitching wedge. One or more additional long irons, such as those designated number 1 or 2, and wedges, such as a gap wedge, a sand wedge, and a lob wedge, may be optionally included with the set. Each iron has a shaft length that usually decreases through the set as the loft for each club head increases from the long irons to the short irons. The length of the shaft, along with the club head loft, moment of inertia, and center of gravity location, impart various performance characteristics to the ball's launch conditions upon impact and determine the distance the ball will travel. Flight distance generally increases with a decrease in loft angle and an increase in club length. However, difficulty of use also increases with a decrease in loft angle and an increase in club length.
Iron-type golf clubs generally can be divided into three categories: blades, muscle backs, and cavity backs. Blades are traditional clubs with a substantially uniform appearance from the sole to the top line, although there may be some tapering from sole to top line.
Muscle backs have a substantially traditional appearance and are similar to blades, but have extra material on the back. This extra material, which may be in the form of a rib, can be used to lower the club head center of gravity. Having the club head center of gravity lower than the ball center of gravity at contact facilitates the golf shot.
Since blade and muscle back designs have a small sweet spot (that is, the area of the face that results in a desirable golf shot upon striking a golf ball), they are relatively difficult to use and are therefore typically only used by skilled golfers. However, these designs allow the golfer to work the ball and shape the golf shot as desired.
Cavity backs move some of the club mass to the perimeter of the club by providing a hollow or cavity in the back of the club, opposite the striking face. The perimeter weighting created by the cavity increases the club's moment of inertia, which is a measurement of the club's resistance to torque, for example the torque resulting from an off-center hit. This produces a more forgiving club with a larger sweet spot. This also allows the size of the club face to be increased, also resulting in a larger sweet spot. These clubs are easier to hit than blades and muscle backs, and are therefore more readily usable by less-skilled and beginner golfers. Other known golf clubs achieve a desired balance or moment of inertia by adding a weight to the club. These clubs typically add a weight member to the bottom surface of the sole, in the center thereof.
Multi-material cavity backs are the latest attempt by golf club designers to make cavity backs more forgiving and easier to hit. Some of these designs replace certain areas of the club head, such as the striking face or sole, with a second material that can be either heavier or lighter than the first material. These designs can also contain deep undercuts, which stem from the rear cavity, or secondary cavities. By incorporating materials of varying densities or providing cavities and undercuts, mass can be freed up to increase the overall size of the club head, expand the sweet spot, enhance the moment of inertia, and/or optimize the club head center of gravity location. However, due to construction limitations or requirements, some of these designs inadvertently thicken the top portion of the club head. Still, these improvements make the multi-material cavity back design the easiest of all styles to hit, and are ideally suited for the less adroit or novice golfer.
As mentioned above, producing a low center of gravity in a club head increases its playability. One of the ways to lower the center of gravity is to lower the face profile of the head. However, this produces a club head with a bad aesthetic appearance. Another method of reducing the club's center of gravity is to reduce the height of the hosel. However, there are disadvantages to reducing the hosel height, such as: reduced moment of inertia (since hosel mass is far away from the center of gravity), shaft-bonding concerns, and the inability to customize the club head via bending for loft/lie. In addition, many golfers dislike the appearance of a club head that has a very small hosel.